Moisture indicators are used, for example, to determine the amount of moisture or humidity in the vicinity of the indicator. Colorimetric indicators change color upon exposure to moisture or humidity. Current commercialized colorimetric moisture indicators are based on cobalt-containing compounds (e.g., CoCl2). Alternatives to cobalt compounds are currently being pursued due to the potential adverse environmental impact and expense of cobalt. Other compositions, such as gel supports that include iron (II), iron (III), or copper chloride salts have also been used as moisture indicators, but these indicators do not show strong absorptions in the visible electromagnetic spectrum and the moisture-indicating color change is often difficult to detect.
Additionally, many colorimetric moisture indicators exhibit the moisture-sensitive color change at only one or two specific moisture levels, limiting each indicator's application. For example, some colorimetric moisture indicators express a color change at 60% relative humidity. Some applications where moisture indication is used require the indicators to be sensitive to higher or lower levels of relative humidity. Additionally, some compositions comprising inorganic salts are inherently unstable to liquid water contact as the salts can readily be transported out of the system.